1. Field of the Invention
The present invention relates to an image format conversion apparatus and method, and, more particularly, to an image format conversion apparatus and method capable of detecting and errorlessly converting horizontally moving text and graphic data of an interlace format contained in images produced in a 3:2 pull-down into images of a progressive format.
2. Description of the Related Art
In general, an image display device employs either the interlace scan mode or the progressive scan mode. The interlace scan mode, which is used for general TVs and the like, divides one image frame into two fields and displays the fields on the screen one after the other in order when displaying one image. At this time, the two fields are referred to as a top field and bottom field, upper field and lower field, odd field or even field, and so on. On the other hand, the progressive scan, or non-interlace scan mode, is used for computer monitors, digital TVs, and so on, and displays the entire frame image at a single time by dealing with one image frame as a frame unit, much like a film is displayed on a screen.
For example, in the case of the 480-line National Television System Committee (NTSC) interlace scan mode (precisely, 487 valid lines in 525 lines), one frame is divided into two 240-line fields for a display, and the 240-line fields divided as such are displayed on a screen one after the other every 1/60 seconds. On the other hand, the progressive scan mode completely displays the entire frame image, a 480-line image, every 1/60 seconds. Accordingly, an image of a progressive format based on the progressive scan mode has a better image quality compared to an image of the interlace format.
One format that is closely related to such a progressive scan mode is a movie produced in film, which is because the original source for almost all recently released DVD movie titles is movies produced in film. Movies are produced at 24 frames per second, which is different from NTSC TV programs. In the case of a DVD movie title, it is, of course, possible to directly manufacture a DVD movie title from original images of 24 frames per second as in an original movie. However, since a majority of image display devices, such as general TVs which are widespread at the present time, adopt the interlace scan mode, DVD movie titles are practically produced in the interlace scan mode, considering such a reality.
Accordingly, a process is required for converting a 24-frame progressive film into 60-field interlace images, which is referred to as the 3:2 pull-down, or the telecine. The 3:2 pull-down process is a process that converts two 24 Hz frames into five 60 Hz fields.
FIG. 1 is a view explaining the 3:2 pull-down process. In FIG. 1, images produced at 24 frames per second in the progressive format are converted into 60 Hz interlace images. That is, as shown in FIG. 1, three fields are produced from the first frame Frame1, two fields are produced from the second frame Frame2, and so on, so five fields are produced per two frames on the whole.
However, since the data exchanges among devices using different scan modes become more necessary than ever as image display devices employing the progressive scan mode increase, an interlaced-to-progressive conversion (IPC) method becomes necessary to convert the interlace scan mode into the progressive scan mode. During such an IPC process, if it is known that a field to be interpolated is for an image of the 3:2 pull-down format, which is produced in 3:2 pull-down interpolation, a complete image of the progressive format before the 3:2 pull-down interpolation can be easily obtained by combining fields of the interlace format. Accordingly, before implementing the IPC method, it becomes necessary to detect whether a field to be interpolated is for an image interpolated in the 3:2 pull-down format. Various conventional methods exist for detecting such images of the 3:2 pull-down format.
However, horizontally scrolling interlaced text, or graphic data such as caption, and so on, may be included in an image of the 3:2 pull-down format. In this case, if the progressive images prior to the 3:2 pull-down interpolation are reproduced by simply combining the interlaced fields without considering scrolling text or graphic data, the text or the like is not smoothly displayed in the interpolated images, and, in worse cases, the broken text is displayed.
Therefore, in the case that an input image is in the 3:2 pull-down format, it is necessary to have an image format conversion apparatus and method capable of detecting whether scroll motions exist on horizontally scrolling interlaced text or graphic data prior to the interpolation, and adaptively interpolating the images accordingly.